1. Field of the Invention
This invention relates to an indicating device in a measuring machine, and more particularly to an indicating device in which the flickering of an indicated value due to vibrations and the like is prevented.
2. Description of the Prior Art
A digital indicating device for digitally indicating a measured value free from personal errors in reading and permitting quick reading, has been widely utilized in various fields of industry.
In general, the digital indicating device of the type described is constructed such that output signals from an encoder operationally associated with a measuring machine are computed, operated and digitally indicated as a measured length in an indication unit formed of liquid crystal and the like.
As the fields of utilization of the measuring machine have widened to the application of feedback signals in a machine tool and higher accuracy has been demanded in the measurement of length, the flickering of the indicated value has become problematical.
For example, as shown in FIG. 1, in a so-called photoelectric linear type measuring machine wherein a main scale 1 and an index scale 3 provided on a slider 2 are moved relative to each other, a change in light quantity due to this relative movement is detected as an electric signal by a detection head 4 and converted into pulse signals, and a measured length is obtained from the pulse signals. Clearance fluctuations between both scales seriously affect the measuring accuracy. In view of this, in order to reduce the lowering in accuracy due to the clearance fluctuations, it is necessary to pressingly retain the interval between both scales through sliding elements 5 and the like for example. However, if the pressing force is excessive, then, when the direction of relative movement is reversed, a return error is increased due to a deflection of a slider support arm 6. In the present status, the fact is that improvements are being made in the method of reducing the adverse influence of the clearance fluctuations, while, the sliding resistance of the slider is being decreased so as to make the return error very small.
In consequence, when the measuring machine is mounted on a machine tool or the like in particular, the indicated value flickers due to the vibrations from the machine tool and it is difficult to read the indicated value. Furthermore, in the indicator of a seven segment system, even if a detected value fluctuates by .+-.1 .mu.m, there are some cases where the indicated value cannot be read at all. For example, when the detected value fluctuates between 99,995 mm and 100,000 mm, there are cases where it is actually read as 188,888. Moreover, the better the sensibility of the measuring machine, the more notably the above-described error appears.
To obviate this disadvantage, there has been known a method in which a renewing interval of samplings of indication data is enlarged as a general technique in the digital indication field. However, this method is not suitable for the measuring machine. The reason is that if tasks of positioning a bite at a predetermined position or the like occur during a measuring process for example, the period of time for confirmation is lengthened to thereby cause troubles.